🐛 Spellcheck comments (#22496)

codespell -q 3 --builtin=clear,rare,informal,code -S ./Marlin/src/lcd/language -L alo,amin,endcode,stdio,uint

Marlin/src/core/macros.h

@@ -399,7 +399,7 @@
     template <typename T, typename ... Args> struct first_type_of { typedef T type; };
     template <typename T> struct first_type_of<T> { typedef T type; };
   }
-  // C++11 solution using SFINAE to detect the existance of a member in a class at compile time.
+  // C++11 solution using SFINAE to detect the existence of a member in a class at compile time.
   // It creates a HasMember<Type> structure containing 'value' set to true if the member exists
   #define HAS_MEMBER_IMPL(Member) \
     namespace Private { \